Compact x-ray generation device

ABSTRACT

An x-ray transmitter, which may be compact, may be in the form of a housing with an x-ray transparent window sputtered with a metal on one wall, and tribocharging electron source on another wall.

BACKGROUND OF THE INVENTION

The present invention relates generally to generation of x-rays, andmore particularly to a tribocharging x-ray transmitter.

X-rays are used in a variety of ways. X-rays may be used for medical orother imaging applications, crystallography related applicationsincluding material analysis, or in other applications.

X-rays are generally generated by electron braking (bremmstrahlung) orinner shell electron emission within a material. Historically, otherthan through natural phenomena, x-rays generally have been generated byaccelerating electrons into a material, such as a metal, with a smallproportion of the electrons causing x-rays through bremmstrahlung orknocking electrons present in the material out of inner orbitals, forexample K-shell orbitals, with x-rays being generated as electrons inhigher energy orbitals transition to the lower energy orbitals.Acceleration of the electrons to generate a useful quantity of x-rays,however, generally requires high powered electrical energy sources,which may include bulky equipment.

X-rays may also be generated by changes in mechanical contact betweenmaterials in a controlled environment, for example through the unpeelingof pressure sensitive adhesive tape or mechanical contact of somematerials in an evacuated chamber. However, changing mechanical contactbetween materials generally involves moving parts within the evacuatedchamber, and generally also requires that some of the moving partsfrictionally contact one another. The moving parts and the frictionalcontact may result in outgassing and production of free debris in theevacuated chamber, possibly impacting operation of such a device.

BRIEF SUMMARY OF THE INVENTION

Aspects of the invention provide an x-ray emitter which may be of acompact design. In some embodiments a small housing, maintaining a lowfluid pressure environment therein, has a first wall with asubstantially x-ray transparent window with an interior coated with ametal and a second wall with at least a portion of an exterior surfaceformed of an electrical insulator, preferably a dielectric material. Themetal on the window provides an electron target, and alternatively theelectron target may instead be positioned within the housing. Theportion of the wall may be the dielectric material itself, or theportion of the wall may be a metal, otherwise electrically insulatedfrom the rest of the housing, with a dielectric exterior covering. Acontacting material, preferably higher in a triboelectric series, is inchanging contact with the exterior covering, with the changing contactpreferably being intermittent contact as well. A filament, preferablyheatable and preferably metallic, is within the housing, for exampleproximate the second wall. In operation contact, removal of contactbetween the contacting material and the dielectric generates a negativeelectrical charge on the portion of the second wall, particularly aninterior surface of the portion of the second wall. Electrons associatedwith the negative charge, and/or electrons provided by the filament maytravel to and impact the metal on the interior of the substantiallyx-ray transparent window, generating x-rays which are emitted ortransmitted through the window.

Some aspects of the invention provide an x-ray emission device,comprising: a housing configured to maintain a low fluid pressureenvironment, the housing having a first wall with a window substantiallytransparent to x-rays and a second wall having a portion comprising anexterior surface comprising an electrically insulating material; anelectron target comprised of a metal within the housing; an electricallychargeable material within the housing; and a contact material forfrictionally contacting the electrically insulating material, thecontact material being lower in a triboelectric series than theelectrically insulating material.

Some aspects of the invention provide a method of emitting x-rays from ahousing, the housing being substantially opaque to x-rays and having achamber at a low fluid pressure, comprising: frictionally contacting anexterior surface of the housing with a contacting surface, the exteriorsurface and the contacting surface being of different materials, wherebya charge imbalance is generated through the frictional contact, withaccumulation of negative charge by the exterior surface; allowing for aflow of electrons, from about an interior surface of the housingproximate the exterior surface contacted by the contacting surface, andtowards a window of the housing; generating x-rays proximate the windowof the housing, the window of the housing being substantiallytransparent to x-rays.

Some aspects of the invention provide a device for emission of x-rays,comprising: a housing configured to maintain a low fluid pressure in achamber within the housing, the housing including a window substantiallytransparent to x-rays but otherwise substantially opaque to x-rays;means for generating a charge imbalance on a portion of the housingthrough changing contact of material external to the housing with asurface of the housing; an electron target within the housing; and afilament within the housing substantially between the portion of thehousing and the electron target.

These and other aspects of the invention are more fully comprehendedupon review of this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates aspects of an x-ray emission device in accordancewith aspects of the invention;

FIG. 2 illustrates a cross section of a portion of a wall of a housingin contact with a contact surface in accordance with aspects of theinvention;

FIG. 3 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention;

FIG. 4 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention;

FIG. 5 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention;

FIG. 6 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention;

FIG. 7 illustrates aspects of the x-ray emission device of FIG. 6; and

FIG. 8 illustrates a mode of operation of an x-ray generation device inaccordance with aspects of the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates aspects of an x-ray transmission device in accordancewith aspects of the invention. The device includes a housing 111, withthe housing configured to maintain a low fluid pressure environment. Insome embodiments the low fluid pressure environment is an environmentwith a pressure less than 200 mTorr, in some embodiments a pressure lessthan 50 mTorr, and in some embodiments a pressure less than 10 mTorr. Insome embodiments a gas, such as Argon, is contained in the housing, withthe gas serving to assist in control of current flow from oppositelycharged surfaces or from a charged surface to ground, and the gas canserve as a source of electrons. Partial pressure of the gas may be, forexample, 50 mTorr, and in various embodiments may be between 1 mTorr and200 mTorr. In some embodiments the housing is generally of a ceramicmaterial.

The housing has a first wall 113 with at least a portion having anelectrically insulating exterior surface, a polyimide film, for exampleKapton, in some embodiments, and preferably a dielectric material. Insome embodiments the portion of the wall having the electricallyinsulating exterior is a membrane formed of the electrically insulatingexterior. In some embodiments the portion of the wall comprises a metal,electrically insulated from other portions of the housing, towards aninterior of the housing, with the electrically insulating materialcovering the metal on the exterior of the housing. In some embodimentsthe portion of the housing comprises a grid of metals, which may in someembodiments be within, upon or floated on other material. In someembodiments the portion of the wall comprises a non-metal, for example aglass or a ceramic material.

A contacting surface 115 is in changing contact with the electricallyinsulating exterior of the housing. The contacting surface is preferablyof a material such that changing contact between the contacting surfaceand the electrically insulating material generates a charge imbalance.Preferably, the material is such that the electrically insulatingmaterial becomes more negatively charged. In some embodiment thematerial is higher in a triboelectric series than the electricallyinsulating material. The contacting surface may be in changing contactwith the electrically insulating material by way of frictional contactof the contacting surface over varying surface areas of the electricallyinsulating material. This may be accomplished, for example, by havingdifferent portions of the contacting surface in contact with differentportions of the electrically insulating material over time, by way ofrepetitive contact and separation of the surfaces, or by way of some orall of the foregoing.

The contacting surface may be moved, or driven, in a variety of manners.In some embodiments, and as representatively illustrated in FIG. 1, thecontacting surface may be driven in a rotary manner, with the contactingsurface coupled to a motor 117 by way of an axle 119. In someembodiments the contacting surface may be driven by a linear motiondevice, with the direction of motion for example parallel to the surfaceof the electrically insulating material or perpendicular to the surface.In some such embodiments the linear movement may be oscillatory, forexample driven by a motor, with the motor having periodically timedreversals of direction or with the motor coupled to the contactingsurface by appropriate direction reversal linkages. In some suchembodiments the linear movement may be applied through circulation of abelt or band, with the belt or band serving as or carrying thecontacting surface. In some embodiments the contacting surface may bedriven by hand operated devices, and in some embodiments be driven byhand driven devices.

In operation, the changing contact between the contacting surface andthe electrically insulating material results in electron accumulation,or negative charging, of the electrically insulating material. Inembodiments in which the electrically insulating material is a membraneforming a portion of the wall of the housing, the membrane becomesnegatively charged. In embodiments in which the electrically insulatingmaterial is an exterior cover for a section of the housing, for examplea metal section, electrically insulated from other portions of thehousing, forming the second wall, the metal becomes negatively charged.The electrons providing the negative charge may travel to and strike anelectron target within the housing.

In the embodiment of FIG. 1, the electron target is a metal on aninterior surface of a window 121 of the housing. The metal, which may begold, may be deposited on the window by sputtering, for example. Thewindow is substantially transparent to x-rays, and may be formed forexample of beryllium. As illustrated in FIG. 1, the window is on a wallof the housing opposite the wall having the electrically insulatingmaterial forming an exterior portion. As the electrons strike the metal,some x-rays may be generated. The x-rays may exit the housing throughthe beryllium window, with the device therefore serving as an x-raygenerator with x-ray emission or transmission capabilities.

FIG. 2 illustrates a contacting surface 215 in contact with anelectrically insulating material 217, for example as in some embodimentsof the device of FIG. 1. In FIG. 2, an axle 211 drives a base 213. Thebase may be wood in some embodiments. The contacting surface 215 isfixed to the base, and therefore is driven along with the base. Thecontacting surface may be, for example, quartz. The contacting surfaceis in changing contact with the electrically insulating material, forexample Kapton. The Kapton is fixed to, and provides an exterior surfacefor a metal 219. As the Kapton tribocharges due to the changing contactwith the contacting surface, negative charge accumulates on a surface ofthe metal away from the Kapton surface, namely on a surface of the metalexposed to an interior of a housing.

FIG. 3 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention. The device of FIG. 3, like thedevice of FIG. 1, includes a housing 311 configured to maintain a lowfluid pressure environment. The housing includes a portion of one wallincluding a membrane 313 of a dielectric material, with in someembodiments the dielectric material covering an exterior of a metal,electrically insulated from the rest of the housing, forming the rest ofthe portion of the one wall. An axle 315 drives a base 317, with thebase having fixed to it a contacting material 321 in changing contactwith the dielectric of the housing. The axle, as illustrated in FIG. 3,is driven by a motor 319.

Interior to the membrane, and interior to the metal underlying themembrane, if present, are field emitting tips 323. The field emittingtips may be, for example, sharp metal tips or carbon nanotubes. In someembodiments the field emitting tips extend from etal pieces interior tothe membrane. In some embodiments there are a plurality of such metalpieces, which in some embodiments are electrically insulated from eachother. In some embodiments one field emitting tip extends from eachmetal piece, in some embodiments one or more field emitting tips extendfrom each metal piece, and in some embodiments a plurality of fieldemitting tips extend from each metal piece. Further, in some embodimentsa conductive mesh may be placed over the field emitting tips, with arelatively low voltage, less than 1000 V in some embodiments, applied tothe conductive mesh to assist in preventing electrical discharge fromthe field emitting tips; with control of the applied voltage serving tocontrol the electron emission from the tips. A heatable filament 325,for example of tungsten or Lanthanum Hexoboride, or alternatively acathode such as a Barium Oxide cathode, is also interior of the housing,preferably proximate the field emitting tips. The heatable filament maybe coupled to an energy source, for example a battery, through ports(not shown) in the housing. The heatable filament provides an electronsource, for example that can be under controlled power from an externalpower supply.

Another wall of the housing, shown opposite the wall with the dielectricin FIG. 3, contains a window 327. The window itself is substantiallytransparent to x-rays, being formed of for example Beryllium. In theembodiment of FIG. 3, however, an interior surface of the window iscovered with a metal, for example gold, forming an electron target,

Operation of the device of FIG. 3 results in negative charging of themembrane, with electrons from the membrane and the filament traveling toand striking the electron target on the surface of the window. X-raysgenerated from this process travel through the window, with the devicetherefore being an x-ray emission source.

FIG. 4 illustrates aspects, in semi-cross-sectional view, of a furtherx-ray emission device in accordance with aspects of the invention. Thedevice of FIG. 4 is similar to the device of FIG. 3, with a housing 411providing for maintenance of a low fluid pressure environment, aBeryllium window 421 on one side of the housing, and a membrane 413forming a portion of an opposing wall of the housing. A contactingmaterial 415, higher in a triboelectric series than the membrane, is insliding linear contact with the membrane, resulting in tribocharging ofthe membrane. Field emitting tips 417 extend from the membrane towardsthe interior of the housing, with a filament 419, for example heatable,between the window and tips of the field emitting tips, and preferablycloser to or proximate the field emitting tips. Negative tribochargingof the membrane allows for accumulation of negative charge at tips ofthe field emitting tips, substantially providing a negative surfacecharge about the tips, and allowing the tips to serve as a cathode. Ametallic interior surface 423 on the window serves as an anode,receiving electrons from filament. As electrons strike the metallicinterior surface, which also acts as an electron target, x-rays aregenerated and transmitted through the window.

FIG. 5 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention. The device of FIG. 5 issimilar to that of FIG. 4, but differs in that the window does not havea metallic coating. Instead, an electron target is in the interior ofthe housing, and not in contact with the window.

In the device of FIG. 5, a housing has a window 525 on one wall, withthe window substantially transparent to x-rays. A membrane, for exampleof Kapton, forms a portion of another wall, with the other wall notopposite the wall including the window. A contacting material 515 is insliding changing contact with the membrane, with the contacting materialhigher in a tribocharging series than the membrane. Field emitting tipsare immediately interior to the membrane, with a filament 519 interiorto the field emitting tips.

A solid electron target 521, for example of a metal, is in the interiorof the housing. The electron target includes a surface 523 having a lineof sight with both the filament/field emitting tips/membrane and thewindow. As the device is operated, electrons from the filament strikethe electron target, generating x-rays, some of which exit through thewindow. Advantageously, in some embodiments the electron target may berotated such that the surface 523 may receive fewer electrons, orrotated so as to emit fewer x-rays towards the window, allowing forincreased control of x-ray flux through the window. Similarly, oradditionally, in some embodiments the electron target may be movedcloser to or farther from the window, also allowing for increasedcontrol of x-ray flux through the window. The distance from the membraneto the target can also be varied, in some embodiments, to change themaximum energy of the striking electrons as a means to control theoutput x-ray energy. The material of the target can be chosen to providea particular x-ray spectrum, with for example the characteristic x-raylines of a material such as Molybdenum. Further, in some embodiments theportion of the housing and the contacting surface, and the fieldemitting tips, may be instead or in addition be placed in reverse, withthese items instead or in addition placed on an opposing side of thehousing and the materials of the exterior of the portion of the housingand the contacting surface reversed. With the materials reversed, inoperation a positive charge is generated, and with the positive chargeattracting electrons from the filament to that opposing side of thehousing, with in some embodiments the electron target in the path ofsuch electrons. In some embodiments, however, the electron target may beelsewhere, for example on an interior surface of the window, with whatmay be considered back scattered electrons generating x-rays in theelectron target, with x-rays emitted through the window.

FIG. 6 illustrates aspects of a further x-ray emission device inaccordance with aspects of the invention. In the embodiment of FIG. 6, ahousing 611 again is configured to maintain a low fluid pressureenvironment. The housing includes a window 621 substantially transparentto x-rays on one wall, with a membrane 613, possibly covering anelectrically insulated metal, on a portion of an opposing wall. Interiorto the housing is a filament 619 to provide an electron source.

The membrane is negatively tribocharged through rolling contact with acontacting material 615. Material of the membrane and the contactingmaterial are selected such that tribocharging occurs through changingcontact of surfaces of the two materials, with the membrane beingnegatively charged compared to the contacting material.

In the embodiment of FIG. 6, a secondary container contains thecontacting material, with the membrane also forming a wall of thesecondary container. The container may be an enclosed container,providing a controlled environment about the contacting material and anexterior (to the housing) surface of the membrane. Preferably thecontrolled environment is controlled so as to prevent electricaldischarge exterior of the housing. In some embodiments the controlledenvironment is at a fluid pressure that reduces discharge, and in someembodiments the container contains a dielectric medium, for examplesulfur hexafluoride, to assist in preventing discharge.

FIG. 7 illustrates an embodiment of a contacting roller 713, which mayalso slide, in contact with a membrane 711. The contacting rollerincludes a first portion 715 of a first dielectric material and a secondportion 717 of a second different dielectric material with a lowerdielectric constant. Each of the first dielectric material and thesecond dielectric material are exposed on the surface of the roller indifferent areas. As the roller rolls across the membrane, the firstportion and the second portion alternate in contacting the membrane.This alternating contact results in variation of compensating charge,with accumulated negative charge on the membrane being ejected as thesecond dielectric material contacts the membrane.

FIG. 8 illustrates a mode of operation of an x-ray transmission devicein accordance with aspects of the invention. In FIG. 8 a housing 811 isconfigured to maintain a low fluid pressure environment. The housingincludes a window 827 on one side of the housing, with the window of amaterial substantially transparent to x-rays. An electron target is onan interior surface of the window. A membrane 813 forms a portion of anopposing wall of the housing, preferably with field emitting tips 823interior to the membrane, and a heatable filament interior to the fieldemitting tips. The membrane is in changing contact with a contactingmaterial 815. Material of the membrane and the contact material areselected such that the changing contact results in negativetribocharging of the membrane.

The contacting material is mounted to a base 817 on a drive system. Asshown in the embodiment of FIG. 8, the drive system includes an axle 819driven by a motor 821, with the axle rotating the base 817. In otherembodiments the contacting material may be otherwise driven.

As illustrated in FIG. 8, the contacting material may be withdrawn fromcontact with the membrane. Once the contacting material is withdrawnfrom such contact, accumulated negative charge is ejected from aninterior surface of the membrane, resulting in electrons flowing fromthe filament to the electron target, generating x-rays which passthrough the window.

Although the invention has been discussed with respect to variousembodiments, it should be recognized that the invention comprises thenovel and non-obvious claims supported by this disclosure.

What is claimed is:
 1. An x-ray emission device, comprising: a housingconfigured to maintain a low fluid pressure environment, the housinghaving a a first wall with a window substantially transparent to x-raysand a second wall having a portion comprising an exterior surfacecomprising an electrically insulating material; an electron targetwithin the housing; an electrically chargeable material within thehousing; and a contact material for frictionally contacting theelectrically insulating material, the contact material comprising amaterial such that frictional contact with the electrically insulatingmaterial generates a charge imbalance.
 2. The x-ray emission device ofclaim 1, wherein the portion of the second wall comprising theelectrically insulating material further comprises a metal interior toand in contact with the electrically insulating material, the metalelectrically insulated from other portions of the housing.
 3. The x-rayemission device of claim 1, wherein the electron target is metal on aninterior surface of the window substantially transparent to x-rays. 4.The x-ray emission device of claim 3, wherein the metal is goldsputtered onto to the window substantially transparent to x-rays.
 5. Thex-ray emission device of claim 1, wherein the electrically chargeablematerial within the housing comprises a heatable filament proximate theelectrically insulating material of the housing.
 6. The x-ray emissiondevice of claim 5, wherein the filament is a tungsten filament.
 7. Thex-ray emission device of claim 1, wherein the electron target comprisesa metal within the housing positioned so as to have at least one surfacein a line of sight of both the window substantially transparent tox-rays and the portion having the exterior surface comprising theelectrically insulating material.
 8. The x-ray emission device of claim1, further comprising field emitting tips within the housing proximatethe portion of the second wall having the exterior surface comprisingthe electrically insulating material.
 9. The x-ray emission device ofclaim 8, wherein the field emitting tips comprise metal tips.
 10. Thex-ray emission device of claim 8, wherein the field emitting tipscomprise carbon nano-tubes.
 11. The x-ray emission device of claim 1,wherein the electrically insulating material comprises a dielectric. 12.The x-ray emission device of claim 1, wherein the electricallyinsulating material comprises a polyimide film.
 13. The x-ray emissiondevice of claim 1, wherein the electrically insulating materialcomprises a membrane.
 14. The x-ray emission device of claim 1 whereinthe electrically chargeable material is a mesh.
 15. The x-ray emissiondevice of claim 1, further comprising a secondary container having atleast one wall sharing at least part of the portion of the second wallhaving the exterior comprising the electrically insulating material, thesecondary container containing the contact material.
 16. The x-rayemission device of claim 15, wherein the secondary container provides acontrollable environment to control discharge.
 17. The x-ray emissiondevice of claim 15 wherein the secondary container further contains adielectric medium.
 18. The x-ray emission device of claim 17, whereinthe dielectric medium is sulfur hexafluoride.
 19. The x-ray emissiondevice of claim 1, wherein the electron target comprises a metal. 20.The x-ray emission device of claim 1, wherein the electron targetcomprises a ceramic compound.
 21. The x-ray emission device of claim 1,wherein the electron target comprises a rare earth compound.
 22. Amethod of emitting x-rays from a housing, the housing beingsubstantially opaque to x-rays and having a chamber at a low fluidpressure, comprising: frictionally contacting an exterior surface of thehousing with a contacting surface, the exterior surface and thecontacting surface being of different materials, whereby a chargeimbalance is generated through the frictional contact, with accumulationof negative charge by the exterior surface; allowing for a flow ofelectrons, from about an interior surface of the housing proximate theexterior surface contacted by the contacting surface, and towards awindow of the housing; generating x-rays proximate the window of thehousing, the window of the housing being substantially transparent tox-rays.
 23. The method of claim 22, wherein the x-rays are generated ina material on an interior surface of the window.
 24. The method of claim23, wherein the material on the interior surface of the window is ametal.
 25. The method of claim 22, further comprising heating a filamentin an interior portion of the housing proximate the interior surfaceproximate the exterior surface contacted by the contacting surface. 26.The method of claim 22, further comprising, repeatedly, withdrawing thecontact surface from the exterior surface of the housing andfrictionally contacting the exterior surface of the housing with thecontacting surface.
 27. A device for emission of x-rays, comprising: ahousing configured to maintain a low fluid pressure in a chamber withinthe housing, the housing including a window substantially transparent tox-rays but otherwise substantially opaque to x-rays; means forgenerating a charge imbalance on a portion of the housing throughchanging contact of material external to the housing with a surface ofthe housing; an electron target within the housing; and a filamentwithin the housing substantially between the portion of the housing andthe electron target.
 28. The device of claim 27, wherein the electrontarget is material on an interior surface of the window.
 29. The deviceof claim 28, wherein the electron target is a metal on the interiorsurface of the housing.